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This is the Strange 2014T-6 Lightweight Aluminum 9-inch assembly for classic Mustangs. There are two basic castings available: N1901 with a 3.0625-inch bearing bore or the N1904 with a 3.250-inch bore. This is more for racing because, due to the flexible nature of aluminum, gear life isn't as long. If you want less weight and superior casting strength, this is a terrific choice.
This is the more common "C7AW" case that first entered service in 1967, good for up to 350 horsepower. This Currie Enterprises' "C7AW" case went into Project Reclaim at Mustangs Plus.
Although your Mustang was originally fitted with sealed axle bearings, the trend today is more toward open bearings lubricated by axle lube. This is quite common with late-model Mustangs with 8.8-inch rear ends.
Free Advice
Use a thread locker, such as Loctite 262, to ascertain fastener security. Conventional and locking differentials have two different bolt lengths. Don't get that mixed up.